The present invention relates to a gas appliance for producing an open flame, and more specifically, to a gas appliance which is durable and includes an automatic gas shut-off device responsive to flame outage so that the gas appliance can operate safely even if left unattended. The present invention also relates to a method of safely producing an open flame wherein a supply of combustible gas is terminated automatically in response to extinguishment of the flame.
Gas appliances capable of producing an open flame are generally known. Such gas appliances are used in places where the accumulation of certain unburned or incompletely burned gases is to be avoided. One such place is the lower area around a typical blast furnace. The lower part of a blast furnace emits carbon monoxide (CO) gas, through openings in the blast furnace. An open flame in the CO gas advantageously keeps the carbon monoxide gas ignited and reduces the level of carbon monoxide around the furnace. It is known that a significant accumulation of CO gas, or any other combustible gas, presents a danger to anyone subsequently entering the area where the gas has accumulated. Not only is there a danger of asphyxiation, but also a danger of explosion if the concentration of the gas reaches high enough levels. Thus, in an effort to prevent such accumulations of CO gas, gas appliances that produce an open flame are placed around the typical blast furnace. The level of carbon monoxide that exists below the blast furnace is too high for humans to breathe for extended periods of time, and therefore, the gas prohibits workers from remaining in that area without the aid of supplemental breathing devices. Since the use of breathing devices requires extensive training, and it involves considerable time and expense to purchase and maintain, such breathing devices, they are not widely used within the industry. It is also very expensive to monitor an open flame gas appliance when they are used around a blast furnace. Iron-makers are reluctant to assign valuable personel to simple monitoring tasks because of high labor costs, and automatic monitoring equipment is both expensive to purchase and expensive to maintain. Such costs make monitoring activities very uneconomical.
Accordingly, such gas appliances have been left unattended at various positions along the underhearth area of a blast furnace. This presents a different danger for iron-makers. If the flame is accidently or unexpectedly extinguished by the gas supply being momentarily interrupted, or by a gust of wind that extinguishes the flame, or for any other reason, the combustible gas is free to accumulate around the blast furnace. Eventually, as has happened in the past, the combustible gas finds an alternative ignition source and explodes, causing serious injuries and damage.
Consequently, there is a need within the industry for a gas appliance capable of providing an open flame, and capable of automatically terminating the flow of gas through the appliance if the flame is extinguished so that the gas appliance can be used safely even if left unattended. Such an appliance must be relatively uncomplicated to reduce manufacturing costs and must be durable to withstand heavy industrial use. It is also necessary to provide a gas appliance that is capable of producing an open flame and that satisfies Occupational Safety and Health Administration (OSHA) requirements and guidelines promulgated by the U.S. Department of Labor. For example, according to 29 C.F.R. .sctn. 1910.110 (c)(5)(h), portable heaters shall be equipped with an approved automatic device to shut off the flow of gas to the main burner, and pilot if used, in the event of flame extinguishment.
Since the need for a gas appliance frequently arises in an industrial environment (e.g., around a blast furnace, construction site, and the like), it is important that a gas appliance be able to withstand the type of abuse found in such of environments. A gas appliance, in this regard, should be able to withstand damage when dropped, and within reason, should be able to withstand crushing when heavy objects are dropped upon it. Hence, there is a need for a gas appliance that not only automatically shuts off the flow of gas when the flame is extinguished, but one that includes a protective member to shield critical elements of the gas appliance from damage (e.g., a gas shut-off valve, a flame or heat sensor associated therewith, and any communication lines extending between the valve and the sensor). Without a protective member or shield, the critical elements of a gas appliance are vulnerable to damage. Damage to such critical elements, in turn, can create significant problems, such as gas leaks, an inability to shut-off the gas when the flame is extinguished, and inoperability of the gas appliance. Notably, the first two of the exemplary problems can pose a significant danger to people and things near the gas appliance.